In some Disk Access Storage Device (DASD) designs particularly at start up, friction and stiction forces significantly resist the rotation of the disk and spindle requiring a more powerful drive motor and, in turn, also requiring larger spaces. In small DASD units, the disk drive motors and actuator motors are sized generally to produce just enough torque to operate the DASD in its worst case or most demanding condition, typically the start up. At start up, the disks must be accelerated and the friction/stiction forces overcome; because the stiction/friction forces may be additive, the drive motor may not be sufficient to overcome these forces to accelerate the disks.
The advantages of unloading the head from the disk surface to prevent stiction and further to prevent damage to the magnetic disk surface are well known. DASD designs commonly include a ramp or inclined surface located generally adjacent the edge of the magnetic disk. An example of such an outer diameter unload/load ramp is illustrated in U.S. Pat. 5,189,575, issued to Onooka, et al. An inside diameter load/unload ramp is disclosed in co-pending application, Ser. No. 08/172,366 filed Dec. 21, 1993, abandoned, by Lowell J. Berg, et al., and commonly assigned herewith. A rotating frustum of a cone load/unload surface is illustrated in U.S. Pat. No. 4,752,848, issued to Garcia, et al.
While the effect of friction or stiction forces between the slider and the magnetic recording disk may be eliminated whenever the slider is unloaded and the disk stopped, relatively significant stiction and friction forces remain, although smaller, between the portions of the load beam and the ramp. In order to reload the slider onto the surface of the magnetic recording disk, the actuator arm must be moved to displace the distal end of the actuator arm away from the unload or parking area. The initial impulse necessary to move the actuator arm to reload the slider onto the disk is large enough that velocity controls must be implemented to reduce both the horizontal and vertical velocity of the slider to prevent disk damage. These velocity controls are expensive to implement.
While the absolute magnitude of forces required to move the load beam relative to the inclined ramp may be quite small, such as illustrated in co-pending application Ser. No. 08/172,366 referenced above, such forces contribute in a very significant way to the load on the actuator motor. As the load beam of the actuator is static in its unloaded position, inertia and friction/stiction forces between the unload tang and the unload ramp combine to resist movement of the load beam and slider towards a region over the surface of the magnetic disk. These same forces also resist start up of the disks whenever the unload tang rests on a surface that rotates with the disk and spindle. Similarly, friction between the surface of the tang and the load/unload ramp tends to resist the unloading of the slider from the surface of the disk and must be accommodated in the sizing of the actuator motor.
In as much as the inclined surface of the load/unload ramp may be a part of spacer rings between adjacent disks in a multi-disk DASD, the tang of the unload device may engage the ramp which is continuously rotating about the axis of rotation with the disks. In a stopped or static condition, the inclined surface and the load beam do not move relative to each other; the stiction forces between the load/unload device on the actuator arm and the surface of the inclined load/unload ramp are significant in the overall force loading of the drive motor. Accordingly, the disk drive motor must be sized with sufficient torque capacity to overcome the stiction forces to restart the disk. An example of such a rotating inclined surface acting as an unload/load ramp is U.S. Pat. No. 4,752,848, issued to Garcia, et al., on Jun. 21, 1988.
An example of a disk drive with the load/unload ramp disposed outside the periphery of the disk surface is described in U.S. Pat. No. 4,933,785, issued to James H. Morehouse, et al., which engages a ramp with a point engagement using a conical member which will increase the forces necessary to move the cam follower relative to the cam due to the potential deformation of the conical member or the ramp at the point of engagement.